This error occurs multiple times in tests:

eZ\Publish\Core\Repository\Tests\Service\Integration\Legacy\ContentTest::testLoadContentInfo}}
BadMethodCallException: Call to undefined method League\Flysystem\Filesystem::flushCache

We call Flysystem's flushCache() when emptying the var directory in the setup factory. Since cache has been moved out of the Flysystem core, we should be able to remove that call.